7.1 Webmail Question?

I have a Server running SUSE 11 sp1 and Zimbra 7.1.3 The server is used only as a webserver and email server. Problem I am having is that when someone goes to "domainname.com" the webmail login comes up instead of the website. If "www.domainname.com" is entered then the website comes up fine, and if the "mail.domainname.com" is entered then the webmail comes up fine as it should. What I need to do is to get rid of the webmail login coming up at the "domainname.com" entry so when someone enters that into a browser without the www the website comes up instead of the Zimbra webmail login. Any ideas on what/where I need to go to accomplish this?